Compound gear and centrifugal pump



y 19, 1955 M. E. CHANDLER COMPOUND GEAR AND CENTRIFUGAL PUMP 3 Sheets-Sheet 1 Filed Dec. 20, 1951 INVENTCDR M I LTON E.

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FIC32 CHANDLER ATTORNEY y 1955 M. E. CHANDLER COMPOUND GEAR AND CENTRIFUGAL PUMP 5 Sheets-Sheet 2 Filed Dec. 20, 1951 FIC5.4

m& umDhmmml July 19, 1955 M. E. CHANDLER COMPOUND GEAR AND CENTRIFUGAL PUMP 3 Sheets-Sheet 3 Filed Dec. 20, 1951 INVENTOR M/lTfl/V 50/4/7015? ATTORNEY United States Patent COMPOUND GEAR AND CENTRIFUGAL PUMP Milton E. Chandler, New Britain, Conn., assignor to Niles-Bement-Pond Company, West Hartford, Come, a corporation of New Jersey Appiication December 243, 1951, erial No. 262,53i 11 Claims. (Cl. Gil-39.28)

This invention pertains to improvements in rotary pumps and more particularly has reference to high speed, high pressure pumps of the centrifugal type, especially adapted to meet the requirements of fuel pumps for aircraft internal combustion engines and gas turbines of the turbo-jet type. Such pumps should have the following general characteristics:

(1) Ability to handle considerable quantities of liquid fuel at moderate or high discharge pressures.

(2) Ability to develop sulficient discharge pressures at low speeds, without developing excessive discharge pressures at high speeds.

(3) High head in a single stage, with small diameter impeller wheel.

(4) Fairly large capacity, with small over-all size and weight.

(5) Simplicity of construction.

Experience with aircraft engine fuel pumps heretofore in use has shown that a single-stage, direct-engine-driven, positive displacement type of pump, such as a gear or vane pump, will develop sufficient discharge pressures at low speeds (e. g. per cent of maximum rated speed), but also develops, at full (100 per cent) rated speed, such high discharge pressures as to cause excessive strain and wear on the pump. On the other hand, a centrifugal type of pump develops proper discharge pressures at high speeds, but insufficient discharge pressures at low speeds. Accordingly, in order to meet the above mentioned requirements, some form of compound pump, or a variable capacity dynamic pumping arrangement is necessary.

With the primary objective of achieving a solution of this problem, without resorting to the use of multiple stage pumps with their attendant complicated control valve mechanisms, I propose to devise, in a single unit, a compound gear and centrifugal pump, having certain auxiliary control features, which enables it to meet the required performance characteristics.

The basic philosophy of my invention is to provide a compound pump comprising a gear pump in series with a centrifugal pump, with the capacity of the former in excess of the capacity the latter pump is called upon to deliver. On the discharge side of the gear pump leading back to inlet, there is a relief valve which is loaded by a variable control pressure from the engine fuel control apparatus. This relief valve is unloaded by the discharge pressure of the centrifugal pump, but the unloading area of the relief valve exposed to the discharge pressure is less than the loading area subject to the engine control pressure. At low engine and pump speeds, the gear pump will produce substantially all the pressure, but as said speed increases the centrifugal pump will take on more and more of the load, until at high speeds the gear pump produces very little pressure and the centrifugal pump most of the pressure. I also provide a bypass check valve around the gear pump, so that in case this pump fails, the centrifugal pump may still suck fuel through the bypass. Connected to the discharge outlet of the gear pump there is a no pressure signal to indicate a drop in pressure if the gear pump fails.

With the foregoing and other objects in view, which may be incident to my improvements, my invention consists in the combination and arrangement of elements hereinafter described and illustrated in the accompanying drawings, in which:

Fig. 1 is a schematic view of the my invention;

Fig. 2 is a central, longitudinal section through a compound pump constructed in accordance with my invention;

Fig. 3 is a cross section on the line 3-3, of the pump shown in Fig. 2;

Fig. 4 is a diagram showing the performance characteristics of my improved pump; and

Figure 5 shows, somewhat diagrammatically, my improved pump, as applied to an aircraft turbo-prop engine having an operatively associated manual (pilots) control and an apparatus for generating a control pressure which regulates the operation of said pump.

Referring first to Figure 5, there are shown the principal elements of an aircraft turbo-prop engine, comprising a supporting casing 5%, an air inlet 51, a multistage air compressor 52, a compressor rotor shaft 53; one each of a number of combustion chambers 54, one of a corresponding number of fuel discharge nozzles 55 connected to a generally circular manifold 56 by means of a conduit 57; a multistage gas turbine 53, a turbine rotor shaft 59 connected to the compressor rotor shaft 53; a tail pipe 60 for discharging combustion gases from turbine 59; a center bearing 61 and end bearings 62 and 63 supported by casing 18, a propeller shaft 64 to which is fixed a propeller 65', and a gear train 66 connecting shafts 53 and 6 for rotating propeller 65, and for operating fuel pump 1 and other engine accessories, at a speed proportional to engine speed.

Fuel pump 1, which is the subject of my invention, is of the variable capacity type, and its delivery of fuel (through a conduit 7 to combustion nozzles 55) is regulated by an engine control pressure (pa) which is generated by a control pressure apparatus 67, operatively associated with engine 50 and a manual (pilots) control 68. Apparatus 67 is connected by a conduit 69 to a source of compressor discharge pressure in the engine, and to a corresponding source of compressor inlet pressure by a conduit 70. The control apparatus 67 is responsive to the pressure differential across the compressor 52, which is an indication of air flow through the engine 50.

A main drive shaft 71 in apparatus 57 is driven by the engine at a speed proportional to engine speed, and a manual control shaft 72 is rotatable in response to movement of a shaft 73, to which is fixed an engine control lever 74 of the pilots manual control 68. Lever 74 is operable in reference to a scale 75 on a fixed quadrant 76, said scale being calibrated in terms of angular degrees in relation to engine speed (R. P. M.)

From the foregoing description, it will be appreciated that the delivery of fuel to the engine by pump 1 is regulated in accordance with the engine control pressure (Po), generated by apparatus 67, in response to the pressure differential across the compressor 52 and other engine operating characteristics, and also in response to movement of manual control lever 74.

Referring now to Fig. l, the reference numeral 1 denotes a fluid-tight casing containing all the elements of my compound pump which comprises an engine-driven gear pump 2, operatively connected in series with a cen trifugal pump 3. The fluid to be pumped enters the pump through an inlet 4, traverses a passage 5, gear pump 2, a passage 6, and centrifugal pump 3, and is discharged through an outlet 7. Connecting inlet pasprincipal elements of the outer casing 1 of the compound angle, helical gears 36 and sage 5 with gear pump discharge'passage 6, are two bypass passages S and 9, in the former of which is mounted a control valve 1b that cooperates with sport-1th: to control fiuid'flow through bypass 8 from passage 6 to passage 5. Valve is actuated by a piston 1i, slidably mounted in a cylinder 12, of which the upper end is 7 act on the opposite sides of piston 12. Mounted in bypass 9' is a check valve which is biased toward closed position by a spring 16 and is adapted to open whenever the gear pump discharge pressure (pa) in bypass passage 9 is less than the pressure (p1) in inlet passage 5. This occurs only in the event of failure of the gear pump 2, in which case the centrifugal pump draws fluid through bypass 9 and continuesto deliver said fluid to the engine. Gear gurnp discharge passage 6 is con" nected by a conduit 17 with a warning signal (not shown) in the cockpit which indicates to the pilot when gear pump 2 has failed.

Referring now to Figs. 2 and 3, it will be seenthat pump comprises: (1) a'central body member 20, which encloses inlet passage 5, gear pump 2, the greater part of impeller3il of centrifugal pump 3, bypass control valve 10, and check valve 15; (2) a left-end closure member 21, which houses'the outer portion of impeller 30 and, together with body member 20,-forms discharge passage. '7; and

(3) a right-end closure member 22, which houses the gear pump driving gears 32 and 33. Left-end member 21-is secured to central body member 20 by a plurality of bolts 23 and right-end member is similarly secured to member 20 'by a plurality of bolts 24, so that the three members 20, 21 and 22'form a single unitary fiuid tight casing 1.

6 from gear pump 2 and discharges into a volute pas sage 31 opening into discharge outlet passage 7. A spur gear 32, keyed to the right end of shaft 25, engages reduction gear 33 which is keyed to a drive shaft 34 of gear pump 2, so that the lattershaft is driven at one fourth of the speed of the former. The right end of shaft is splined to gear 35 which is driven by the engine 7 at engine speed.

Gear pump 2 comprises two inter-meshing shallow- 37 which are iournalled in floating, pressure-loaded sleeve bearings 38 and 39, mounted in the lower part of body member 20. Gear 36 is splined to shaft 34 and drives idle gear 37. A seal 40 prevents escape of fluid from the end of bearing sleeve 39. Bearing 33 is loaded by a spring pressed end bearing 41 and the discharge pressure (12d) of gear pump 2 which is transmitted from passage 6 by a duc ,42 to an annular space 43 between the radial flange of sleeve 38 and body member 20.

Slidably mounted transversely in the upper part of body member, 20 is a stem 44 to which are integrally attached piston 11 and two valve heads, 45-h and 45-b,

that together constitute the control valve 10 shown in Fig. l. Valves 45a and 45-h, respectively cooperate impeller 30 of centrifugal pump 3 which communicates with passage biases valve 10 toward open position (i. e., to the right); in opposition to the difference between the compound pump discharge pressure (pa) (from passage 13), and the variable control pressure (pm) (from passage 14), that act on piston 11. But the difference in area between valves 45-!) and S-a is'less than the area of piston 11, so that the unit pressure differential (pzp1) between passages 6 and Srnust exceed the unit pressure differential (pdpc) acting on piston 11, in order to open valve 10. Valve 10 is thus loaded by the variable control pressure (pc) in conduit 14 from control a paratus 67, and said valve isunloaded by the centrifugal pump discharge pressure (pa) in conduit 13 from dis charge passage 7.

Referring now to the chart in Fig. 4, in which the ordinates denote the pump discharge pressures. in pounds per square inch (p. s. i.), and the abscissas denote the speed of the engine and centrifugal pump 3, in

revolutions per minute (R. P. M.), it will be noted that the dotted curve A indicates the speed-pressure characteristic of gear pump' 2, as modulated by the operation of bypass control valve 10; the dotted curve B indicates the speed-pressure characteristic of centrifugal'pump 3; and the full line curve C, indicates the speed-pressure characteristic of the compound pump; all in the'range from zero speed to maximum rated engine speed (e.'g. 24,000 R. P. M.). At low engine and pump speeds (circa-10 per cent of maximum rated speed), pump 2 produces substantially all of the compound pump pressure (pd), but as the engine and pump speed increases, the centrifugal pump 3 takes on more and more of the pumping load, so that at high speeds the gear pump with ports 10:: and 10b which respectively connect gear pump'discharge passage 6 to bypass'passages 8-u and 8-b that together constitute bypass passage 8 'of Fig. 1. As

"shown in Fig. '3, valve -4S"b is larger than 45 1: so that the gear pump discharge pressure (122) in passage 6 a magnitude equal to or greater 2 produces very little pumping pressure, while the cen:

trifugal pump 3 produces most of said pressure. The gear pump 2 and centrifugal pump 3 are that the former, which runs at one-fourth of the speed of the latter, has sufiicient capacity to deliver the required fuel at low speeds (circa .10 per cent of maximum rated engine speed). Thus for example, the gear pump 2 maybe designed to deliver a fuel flow of 4,000 pounds per hour, (P. P. H.) at a pressure (p2) of 165 p. smi. at 2,400 R. P. M. (10 per cent speed).

As the speed of the engine and drive shaft 25 increases, th'e'pressure rise created by the compound gear and centrifugal pump increases and eventually reaches by the engine fuel feed regulator. When this point is reached, the fuel control valve 10 starts to open and that portion of the gear pump output which is not required by the engine is by-passed around the gear pump through passage 8 by the control valve 10. At per cent of I the maximum rated engine speed (e.-g. 24,000 R. P. M.), the gear pump iflow capacity is greater than the fuel required by the engine .at that time (e. g. 40,000 P. P. 11.), so that the whole engine fuel requirement is fed to'the centrifugal pump 3 through the gear pump 2, with a portion being by-passed through control valve 10.

As a result of the above described arrangement, the discharge pressure (p2) of gear pump .2, which is set at say p. s. i. at 2,400 R. P. M., progressively decreases with increasing engine speed, as shown by curve A in Fig. '4, until said discharge pressure 12) is reduced to zero at maximum rated engine speed (24,000 R. P. M.). On .theotherhantl, the discharge pressure (p3) of the centrifugal pump 3, which is approximately 10 p. s. i. at

operate in series, their respective discharge pressures (p2) and (p3) are additive, so that the ordinate of any speed point in the compound pump curve C in 'Fig. -4 is ilte -sum -of theordinates of points incurves A iand B at the same speed point. Since control valve 10 is the gear so arranged 7 than that called for.

responsive to the pressure differential (p2-p1}(pdpc), by a proper choice of areas of valves 45-a and 45-b, and the area of piston 11, the speed-pressure characteristic of gear pump 2, may be modulated, as indicated in curve A of Fig. 4, and a desired speed-pressure characteristic, of the compound pump may be thus obtained, as indicated by curve C of Fig. 4. Thus for example, if it is desired that the compound pump develop a discharge pressure of 175 p. s. i. at 2400 R. P. M. per cent of maximum rated engine speed), and the centrifugal pump creates a discharge pressure (p3) of 10 p. s. i. at that speed, the operation of valve 10 may be made such as to give a gear pump discharge pressure (p2) of 165 p. s. i., as indicated by point D in Fig. 4, so that the compound pump discharge pressure (pd) will be 175 p. s. i., as indicated at point B in Fig. 4. Since the gear pump discharge pressure 12) is reduced to zero at 100 per cent of maximum rated engine speed, curves B and C will coincide at maximum rated engine speed, as indicated by point F in Fig. 4.

From the foregoing description, it is clear that my improved compound pump may be made to have any speed-pressure characteristic as is necessary to deliver the proper amount of fuel for all engine speeds and other engine operating conditions which are controlled by the fuel control apparatus 67, from which the variable control pressure (Po) as indicated in Fig. 1 is obtained. It is further apparent that the novel arrangement of gear pump, centrifugal pump, control valve, and

other elements of my invention, disclosed herein, provides in a single compact unit, a compound pump having the requirements of an aircraft fuel pump, as indicated in column 1, lines 22 to 31.

While I have shown and described the preferred embodiment of my invention, I desire it to be understood that I do not limit myself to the precise details of construction disclosed by way of illustrations, as these may be changed and modified by those skilled in the art without departing from the spirit of my invention or exceeding the scope of the appended claims.

I claim:

1. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine, and means, responsive to a variable control pressure from said engine, for varying the discharge pressure of said compound pump in accordance with a preselected ratio between the discharge pressure and speed of said compound pump throughout the operating speed range of said engine.

2. A compound pump according to claim 1, including means for modulating the discharge pressure of said gear pump in accordance with the unit differential pressure between the discharge pressure of said compound pump and said control pressure.

3. A compound pump according to claim 2, wherein said modulating means is responsive to the pressure rise across said gear pump opposed by said differential pressure.

4. A compound pump according to claim 3, including a by-pass passagefrom the discharge to the inlet side of said gear pump and said modulating means comprises a valve means for regulating the flow through said by-pass passage.

5. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine, means, responsive to a variable control pressure from said engine, for varying the discharge pressure of said compound pump in accordance with a preselected ratio between the discharge pressure and speed of said compound pump throughout the operating speed range of said engine, and means, responsive 5 to the pressure rise across said gear pump, for maintaining a flow of fuel from the inlet of said gear pump to the inlet of said centrifugal pump, in the event of failure of said gear pump.

6. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine, means, responsive to a variable control pressure from said engine, for varying the discharge pressure of said compound pump in accordance with a preselected ratio between the discharge pressure and speed of said compound pump throughout the oper ating speed range of said engine, and means, responsive to the discharge pressure of said gear pump, for indicating to the operator of said engine, a failure in the operation of said gear pump.

7. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine, means for driving said centrifugal pump in a constant higher multiple speed ratio with said gear pump, and means, responsive to a variable control pressure from said engine, far varying the discharge pressure of said compound pump in accordance with a preselected ratio between the discharge pressure and speed of said compound pump throughout the operating speed range of said engine.

8. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine, and means, responsive to a variable control pressure from said engine, for varying the discharge pressure of said compound pump in accordance with a preselected ratio between the discharge pressure and speed of said compound pump throughout the operating speed range of said engine; said gear pump comprising a pair of intermeshing gears, each journalled in an axially movable sleeve bearing having an annular flange contacting the side face of its adjacent gear, and means for subjecting the opposite side face of said flange to the discharge pressure of said gear pump.

9. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine; and means, responsive to the differential of the discharge pressure of said compound pump and a control pressure from the engine, for coordinately controlling the simultaneous discharge rates of said gear and centrifugal pumps so that, at the low end of the engine speed range below a selected speed, the gear pump carries substantially all of the total pumping load and produces substantially all of the discharge pressure of the compound pump, while above said selected speed, the centrifugal pump carries a progressively increasing percentage of the total pumping load and produces a progressively increasing percentage of the discharge pressure of the compound pump, so that at the higher end of the engine range, the centrifugal pump carries substantially all of the total pumping load and produces substantially all of the discharge pressure of the compound pump.

10. A compound pump according to claim 9 wherein, near zero engine speed, the gear pump carries all of the total pumping load and produces all of the discharge pressure of the compound pump; while at maximum speed, the centrifugal pump carries all of the total pumping load and produces all of the discharge pressure of the compound pump.

11. A rotary compound fuel pump for an internal combustion engine, comprising, in a single unit, a gear pump and a centrifugal pump arranged in series and driven through a common drive shaft by and in constant speed ratio with said engine; said gear and centrifugal pump being so'arranged-and coordinated that, at the low end of theuengine speed range below a selected speed, the gear pump carries substantially all ofthe total pumping load and'prodnces substantially all of the discharge pressure 7 of the compound pump, while above said selected speed,

the centrifugal pump carries a progressively increasing percentage of the total pumping load and produces a prosure of the compound pump, while at maximum speed, the centrifugal pump carries all of the total pumping load and produces all of the discharge pressure of the compound pump; said compound pump having means,

responsive to a variable control pressure from the engine, causing the gear and centrifugal pumps to operate' in the specified manner.

References Cited in the file of this patent UNITEDSTATES PATENTS 2,146,184 High Feb. 7,1939 2,443,527 Wirth et ,al. r June 15, 1 948 2,451,055 Beacham Oct. 12, 1 948 2,522,890 Peterson Sept. 19, 1950 2,636,553

Ballantyne et a. Apr. 28, 1953 

